Skirting For Ground Level Of Elevated House

I am using 7.5cm C-Pac blocks on the outside and red brick on the inside with an air gap for all perememter walls. We have a portion of the house 1.2 meters above the ground and I will be blocking this as well. Roofing is Trilon cool roof in a light blue with custom made gable louvers that go the entire rake of roof, instead of those cheesy small gable vents that are readily availbable. I will also use vented soffit all around the house. I want to make sure the underneath part of the house stays as cool as possible. My question here is...I have two ways to underskirt the bottom part. One is use more C-Pac, costing a lot more, or using the thin larger concrete block used for making perimeter walls and putting a radiant barrier with it. Anyone have any input on this? I was thinking of setting those vented blocks used in most Thai bathrooms up high on this bottom part as well. Anyone have any input on this?